The pituitary hormone vasopressin, long known as an antidiuretic hormone, seems to be involved in memory functions. Animal studies and preliminary human studies suggest that vasopressin may reduce the memory impairment caused by ECT; memory impairment is the most common and troublesome side effect of ECT. The purpose of this study is to determine whether administration of vasopressin to patients receiving bilateral ECT can reduce the anterograde ad retrograde amnesia that alsmost invariably occurs. Subjects. Subjects will be 40 inpatients with a DSM-III diagnosis of Major Depressive Episode who are referred for bilateral ECT treatment. Patients will be excluded if they have received ECT within a year or if they have any known organic impairment or contraindications to vasopressin. Methods. Patients will be randomly assigned to receive vasopressin or placebo, double-blind. Total daily dosage of lysine-8-vasopressin (Vasopressin-Sandoz) will be 2 puffs of the nasal spray, or approximately 4.0 Posterior Pituitary Units (PPU) per nostril, QID (this is essentially the highest dose recommended in the PDR for the treatment of diabetes insipidus). The vasopressin will begin just prior to the first ECT and will be given through the dose following the fifth ECT. ECT electrode placement will be bitemporal; bipolar brief pulses with a constant current of 800 ma using the MECTA machine will be administered to induce seizures. If EEG-monitored seizure duration is less than 25 seconds, the electrical stimulus will be repeated at higher settings to give a combined seizure duration of at least 25 seconds. Memory testing, to be completed at baseline and the day after the fifth ECT will include the Quick IQ Rey-Osterreith Complex Figures, TV Test, and two tests from the Wechsler Memory Scale (Paired Words and Digit Span). In addition, to evaluate vasopressin effects on very short-term retrograde amnesia, word lists will be presented just prior to the fourth ECT, and recall tested the next day. Data analysis will compare the vasopressin and placebo groups. If vasopressin is effective in reducing amnesia, given its minimal side effects, it could become clinically important for patients receiving ECT.